1. Field of the Invention
The present invention relates to a control of a motor vehicle, and more particularly to a constant speed motor vehicle control wherein the motor vehicle is controlled to run under a substantially constant speed.
2. Description of the Prior Art
It has already been proposed to provide a motor vehicle with control means for controlling the engine output so that the vehicle is operated with a substantially constant running speed. For example, the Japanese patent application disclosure No. 57-191431 discloses a vehicle control system including desired speed setting means for setting a desired speed, memory means for memorizing the desired speed and controlling means for controlling the engine throttle valve position in accordance with the difference between the desired speed and the actual speed so that the vehicle speed is controlled to the desired value. In more detail, the engine throttle valve is opened when the actual speed is lower than the desired valve whereas the engine throttle valve opening is decreased when the actual vehicle speed is higher than the desired value.
It should, however, be noted that, even when the difference between the actual speed and the desired speed is the same, the required engine output power for recovering the vehicle speed to the desired value will change depending on the value of the desired speed at which the vehicle is to be operated. Further, the road condition such as the slope of the road on which the vehicle is running and the smoothness of the road as well as the wind condition may also affect the required engine power. The system in the prior art does not however take into account the required engine power for attaining the desired or target vehicle speed.